1. Field of the Invention
This invention relates to an apparatus for mounting a torsion spring on a spring support. This invention particularly relates to a torsion spring mounting apparatus which effects the reliable engagement of a torsion spring with its support.
2. Description of the Prior Art
Torsion springs are widely used as urging means in various types of apparatuses. For example, torsion springs are used as urging means for guard panels in video tape cassettes. The torsion spring is mounted on a spring support with a coiled portion of the torsion spring being fitted onto a cylindrical shaft of the spring support.
FIG. 4 is a perspective view showing a conventional torsion spring mounting apparatus. With reference to FIG. 4, a torsion spring 1 is mounted on a supporting means 3 of a guard panel 2 which serves as a spring support. An edge of the guard panel 2 is supported on a fixture 5, and the guard panel 2 is positioned on a base plate 6. The supporting means 3 comprises a cylindrical shaft 3A, and a coil engaging protrusion 3B embedded in the circumferential surface of the shaft 3A such that the coil engaging protrusion 3B is normal to the shaft 3A. On the other hand, the torsion spring 1 comprises an approximately linear leg portion 1A, a coiled portion 1B, one end part of which extends to the leg portion 1A, and an engagement portion lC which extends to the other end part of the coiled portion 1B in the radial direction of the coiled portion 1B. A single torsion spring 1 is fed from a torsion spring feed means (not shown), grasped by claws 7A and 7B of a spring movement means 8, and then fitted onto the supporting means 3. Specifically, after grasping the coiled portion 1B of the torsion spring 1 as illustrated, the spring movement means 8 adjusts the position of the coiled portion 1B so that the center axis of the coiled portion 1B coincides with the center axis of the shaft 3A. Thereafter, the spring movement means 8 moves the torsion spring 1 in the direction indicated by the arrow A along the center axis of the shaft 3A, and fits the coiled portion 1B onto the shaft 3A. At this time, the engagement portion 1C of the torsion spring 1 is positioned in such a way that it does not overlap the coil engaging protrusion 3B of the supporting means 3 in the direction along which the torsion spring 1 is moved.
FIGS. 5A and 5B are perspective views showing how the torsion spring 1 is made to engage the supporting means 3 with the help of gravity. As shown in FIG. 5A, the torsion spring 1 is moved by the spring movement means 8 until the coil engaging protrusion 3B is located between the engagement portion 1C and the coiled portion 1B. Thereafter, the spring movement means 8 moves the claws 7A and 7B away from each other and is retracted upwardly. The center of gravity of the torsion spring 1 is closer to the leg portion 1A than the center point of the coiled portion 1B. Therefore, when the torsion spring 1 is released from the claws 7A and 7B after it is in the position illustrated in FIG. 5A, it is rotated in the direction indicated by the arrow B around the shaft 3A under the force of gravity. As shown in FIG. 5B, as the torsion spring 1 is thus rotated, the engagement portion 1C falls down and engages with the coil engaging protrusion 3B. Thereafter, the guard panel 2 is sent to the next process together with the fixture 5.
As described above, with the conventional technique, after the torsion spring 1 is fitted onto the shaft 3A, engagement between the engagement portion 1C and the coil engaging protrusion 3B is effected by the force of gravity on the leg portion 1A. However, in cases where the torsion spring 1 is mounted quickly, engagement failures readily arise. Also, in cases where the shape of the torsion spring 1 is changed so that the center of gravity of the torsion spring 1 shifts toward the center point of the coiled portion 1B, the engagement portion 1C cannot reliably be made to engage with the coil engaging protrusion 3B.